Assumed Health Care Cost Trend Rates (Detail)	12 Months Ended
Mar. 31, 2015
Pre Sixty Five Coverage
Schedule of Pension Expected Future Benefit Payments [Line Items]
Accumulated postretirement benefit obligation	7.90%
Net periodic postretirement benefit obligation	8.20%
Ultimate health care cost trend	4.50%
Ultimate year health care cost trend rate is achieved	2029
Net periodic postretirement benefit obligation March 31, 2016	7.90%
Post Sixty Five Coverage
Schedule of Pension Expected Future Benefit Payments [Line Items]
Accumulated postretirement benefit obligation	6.90%
Net periodic postretirement benefit obligation	6.90%
Ultimate health care cost trend	4.50%
Ultimate year health care cost trend rate is achieved	2029
Net periodic postretirement benefit obligation March 31, 2016	6.90%

Defined Benefit Plan Assumed Health Care Cost Trend Net Periodic Postretirement Benefit Cost

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- Definition

Defined Benefit Plan Assumed Health Care Cost Trend Postretirement Benefit Obligation

+ References

No definition available.

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- Definition

Defined Benefit Plan, Ultimate Health Care Cost Trend Rate, Postretirement Benefit Obligation

+ References

No definition available.

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- Definition

Defined Benefit Plan Year That Rate Reaches Ultimate Trend Rate Postretirement Benefit Obligation

+ References

No definition available.

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- Definition

The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (l)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Health Care Cost Trend Rate

-URI http://asc.fasb.org/extlink&oid=6514820

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